Because they didn't want to kill him. Just ruin his campaign.
Which didn't work, but I think that was the goal. They got a lot of people at the ceremony for ACB's nomination. A breakout of that magnitude in a "clean" area implies shenanigans.
I suppose that’s one theory. Another theory is that Republicans are out living their lives and running the economy while Democrats are still cowering in their homes/apartments or venturing out in their plastic bubbles.